Method of coating thin flat dielectric plates



May 29, 1956 B. L. JOYNER 2,743,032

METHOD OF COATING THIN FLAT DIELECTRIC PLATES Filed Oct. 8, 195:5

k2 5 [IL :2: n FIG] Z FIG 4 q 6 f mLi ZiVTOR BY M ATTORNEY United States Patent ice METHOD OF COATING 'FLA T DIELECTRIC PLATES Bobby L. JoynergErie, Pa., assignor to'E-rie Resistor Corporation, Erie, Pa., a corporation of Pennsylvania Application October 8, 1953, Serial-N0; 384,839

Claims. (Cl. 117-213) This invention is intende'cl toproduc'e' thin fiat dielectric plates and is particularly advantageous in' producing plates which are of such small size as to be inconvenient to handle manually. When the dielectric plates are ceramic, the plates can be stacked under pressure Without breaking, which is advantageous in high capacity electrical condensers and in piezo-electric devices such as microphones and phonograph pickups. In the manufacture, the fired ceramic plates which may have become warped or distorted during firing, are'arranged side'by side in a mold which is filled with a casting compound thereby producing a casting in which a plurality of the plates are anchored. The casting is then surface abraded on both sides, bringing the casting with the plates embedded therein to the desired finished'thickne'ss' with both sides being flat and parallel to each other. The opposite surfaces of the casting can then be coated with a metal paint, such as one of the silver paints used in the ceramic decorating art, and upon firing, the flat surfaces will-be metallized throughout and the casting compoundwill'beconsumed so that the ceramic plates are no longerheld together but are separate pieces metallized on opposite faces and ready for assembly into the finished product, whether it be an electrical condenser or a piezo-electric device. Before" firing, the casting can be given a preliminary drying operation and the ceramic pieces with the dried paint thereon can be separated from the casting by breaking the plastic away to leave individual ceramic pieces which can then be fired to set the paint. Because the edges of the plates are embedded in thecasting compound'while the metal paint is being applied, there is no danger of short circuiting the metal coatings by paint flowing over the thin edges. The method'is particularly advantageous in the manufacture of very thinceramic plates having a thickness of the order of l0mils.

In the accompanying drawing, Fig. 1 is a top plan-view of aceramic plate such as used in a phonograph pickup; 2 is a section on line 2-2 of Fig. 1; Fig.- 3 is a top plan view of a plurality of fired ceramic plates cast side by side in a plastic disk; Fig. 4 is a section through the mold in which the Fig. 3 disk is cast; Fig. 5 isa diagrammatic view showing Warped fired ceramic plates east side by side in plastic and illustrating the manner in which the plates are held while opposite faces are ground flat to the desired finished thickness; Fig. 6 is a top plan view of the finished'disk after opposite faces have been ground flat; Fig. 7 is a section on line 7-7 of Fig. 6; Fig. 8'isa diagrammatic sectional view of a semi-planetary lapping machine for lapping opposite faces of the Fig. 3 casting flat; Fig. 9 is a top plan view of the Fig. 8 lapping'machine with the top plate removed; and Fig. 10 is a frag mentary section showing one of the composite castings in position for lapping.

The invention is shown applied to the production of barium titanate ceramic plates such as used in the manufacture of phonograph pickups. narily be from to A; of an inch wide and from of an inch to an inch long with a thickness of the order of These plates will ordi- 2,748,032 patented May 29, 1956 2. %b cf'an'inch. In Fig. 1 a top plan view of one of the plates is indicated byfthe reference numeral. 1. In Fig. 2 the plate is shown ready forassembly into a pickup with-metallized coatings land 3 on opposite faces. Because the pickup is a: low'voltage'd'evice, the coatings 2 and 3' cover the entire areaof the opposite faces but do not short ci'rcuitthe I'Omil edge faces 4. When assembled into a-complete pickup,, two of the plates 1 with the silver coatings 2 and' 3 thereon. are soldered back to back to-form a bimorph and are polarized by applyingia high polarizing. voltage from the common. or soldered coatings to the outer coatings after whiclithe assembled pickup. is assembled into a cartridgefor mounting; into a tone arm. Bimorph pickups are well known-andneed not be illustrated for the purpose of this applicatione The plates l with the metal co'atingszand 3 thereon also serve as electrical condensers and other uses areknown.

The small size ofthe plates l rnake them very difficult to handle. Furthermore. as illustrated in Fig. 5, the plates are likely to be warpedboth crosswise andlengthwise during firing and because of the warpage the plates asfired are likely to be broken when the metal paint coatings are applied or when the plates are stacked, as isdesirable in a phonograph pickup and in multi-plate electrical condensers. For this=reason, when flatten mil plates-are desired, the plates are made much thicker, e. g., 25 milsiand opposite; faces are then=ground down to the required thinness; The: srnall size and the shape of the plates-make the grinding a difiicult operation. I

border toget the. plates linto'a form in which they canbe conveniently handled for the grinding operation, theplatesare arranged side by side in a mold cavity 5 which is then filled with one ofthe casting resins such as an unsaturated polyester oran epoxy resin. Fillers such as powderedmicamay be added to the resins to increase the mechanical strengthof the resin and to decrease-the time required forthesubsequent grinding operation. These casting. resins belong to the class of solventless. varnishes and set up by polymerization Without the evolution of moisture The settingup is speeded up byheat and usually by the addition of a catalyst. The casting resins are well' known in the art-and the selection of the particular resinisa matter of engineering. The shapeand size of the. moldcavity 5 obviously depends upon the size of the plates. 1 and upon the equipment to be used for grinding opposite faces. The particular cavity illustrated, which is designed for a lapping machine, is circular and has a diameter somewhat greater than the length of the plates 1 so that approximately ten of the plates may be arranged side by side in the cavity. At the end of the casting operation, the plates are cast in and embedded in a plastic disk having a thickness slightly greater than the fired thicknessof the plates. For example, if the plates when fired are 25 mils thick, the plastic disk may have a thickness of 30 mils. As shown in Fig. 5, the upper and lower surfaces 6- and 7 of the plastic disk are flat and the plastic covers the top and bottom faces of the plate 1 as Well as filling the space 8 between adjacent edges of the side by side plates. While the warping of the plates 1 is greatly exaggerated in Fig. 5, it is evident that grinding away the top and bottom faces 6 and 7 of the plastic disk to the lines 6a and 7a will result in the finished disk shown in Figures 6 and 7 where the plates 1 have opposite faces ground fiat and flush with the faces 6a and 7a and the thickness of the plates, the distance between the faces 6a and 7a, is the desired thickness of the finished plates.

In order to fix metal electrode coatings 2 and 3 to opposite faces of the plates 1, the metal paint, such as one of the silver ceramic paints, is applied over the entire area of the faces 6a and 7a of the finisheddisk. Since the faces 6a 'and7a are fiat, there is no'danger of breaking the brittle ceramic plates by using a squeegee to apply the paint. Dip or spray coatings may be used. After applying the paint, the disk is given a preliminary drying operation and the coated ceramic plates with the dried paint films thereon may then be separated from the disk by breaking away the plastic. Throughout the grinding operation in which the thickness of the cast plastic disk is reduced from that shown in Fig. 5 to that shown in Fig. 7 and throughout the subsequent application of the metallic paint to the faces 6a and 7a, the ceramic plates 1 are securely anchored in the plastic 9 which so holds the plates that they are easy to handle. After both of the faces 6a and 7a have been coated, the plastic disks are fired at the temperature at which the silver paint particles sinter to form a metallic film on opposite faces of the plates 1. During this firing operation which is carried out at a relatively high temperature, e. g., 1100 degrees F., the plastic 9 is consumed, leaving only the individual plates 1 with the metallized coatings 2, 3 on opposite faces thereof. Of course, if the ceramic plates are separated from the plastic before firing, there will be no plastic present during the firing of the individual ceramic plates. Since these plates have been ground flat on opposite faces, they may be stacked for the manufacture of multiple plate electrical condensers or may be arranged back to back for the construction of phonograph pickups of the bimorph type.

In Figs. 8, 9 and 10 is shown a semi-planetary lapping machine for simultaneously grinding the upper and lower faces 6, 7 of the plastic disks. This machine comprises a stationary lower bed 10 having a flat upper surface 11 and a floating upper bed 12 having a flat lower surface 13. The upper bed is loose and is urged downward solely by its own weight and is confined to a position substantially in line with the lower bed 10 by a plurality of spring pressed plungers 14 arranged around the periphery of the upper bed 12. Between the upper and lower beds 10 and 12 is a disk or carrier 15 of flexible plastic, such as one of the vinyl resins, having a thickness substantially equal to the finished thickness of the plastic disks. If the lapping is carried out in two stages, with the first lapping operation bringing the thickness to mils and the second lapping operation reducing the thickness to 10 mils, a thicker carrier 15 may be used for the first lapping operation. At the center of the disk 15 is a vertical drive pin 16 fixed to the disk by a screw 17 threaded into its lower end and having its upper end rotatably receiving a depending crank pin 18 on a shaft 19 suitably driven by means not shown in a drive head 20. The shaft 1% is substantially concentric with the upper and lower beds 10 and 12 so that as the shaft 19 is rotated the flexible disk 15 is given an orbital movement about the shaft 19; that is, the drive pin 16 follows the path indicated by the circle 21. Around the outer part of the disk 15 are a plurality of holes 22 of slightly larger diameter than the outside diameter of the plastic disks which are to be lapped. This means that the plastic disks when received in the holes 22 are free to rotate therein. The orbital movement given the flexible disk 15 is of sufficient amplitude so that the openings 22 progressively move past the inner and outer edges 23 and 24 of the lower bed 10. Throughout this movement, there is a slight precession of the disk 15 around the center of the drive shaft 19 but at a much slower rate than the rotation of the drive shaft, and there is also a turning of the plastic disks within the openings 22 which is desirable because it insures that all parts of the plastic disks will be subjected to substantially the same lapping action. At the start of the lapping operation, the plastic disks which are indicated at 25 will be much thicker than the thickness of the flexible disk 15 but at the end of the lapping operation the upper and lower faces of the plastic disks 25 will both be lapped to reduce the thickness of the disk to substantially that of the flexible disk 15.

The lapping machine illustrated in Figs. 8 to 10 is representative of the grinding or surface abrading machines useful for grinding the faces 6, 7 of the plastic disks down to the thickness indicated by 6a, 7a in Fig. 5 and thereby to produce accurate flat faces on opposite sides of the ceramic plates 1. Lapping is perhaps the most precise of the surface abrading operations and may not be necessary if less precision is required.

For silvering the flat ceramic plates, it is not necessary that plastic be used for embedding the ceramic plates. A cement like material such as plaster of Paris may be used. The plaster of Paris will keep the silver paint from running over the edges of the ceramic plates in the same manner as the plastic and will disintegrate at the firing temperature of the silver paint, leaving the ceramic plates metal coated over the entire surface of the opposite faces but without any metal coating on the edges. Plaster of Paris does not have the mechanical strength necessary for the lapping or grinding operation.

What I claim as new is:

1. The method of making thin flat ceramic plates having a thickness small compared to both length and width which comprises casting a plurality of spaced apart fired ceramic plates of greater than finished thickness flatwise side by side with adjacent edges of plates out of contact with each other in a flat body of plastic thicker than the plates to produce a composite plastic body having the ceramic plates with edges and opposite faces embedded therein and with opposite faces of the ceramic plates generally parallel to opposite faces of the plastic body, grinding away opposite faces of the composite plastic body to a depth below the opposite faces of the ceramic plates to produce a flat composite plate with both the plastic and ceramic ground to said finished thickness of the ceramic plates and with the edges of the ceramic plates held therein and with opposite faces of the ceramic plates flush with the ground surfaces, coating both the plastic and ceramic portions of the opposite faces of the composite plate with a metal ceramic paint of the type settable by firing to a metal coating, and firing the paint coated faces to burn away the plastic and to set the paint to the ceramic plates.

2. The method of applying metal electrodes to the entire area of opposite faces of a plurality of spaced apart ceramic plates without short circuiting over the edges which comprises embedding the edges of a plurality of side by side ceramic plates flatwise in a body of plastic with the opposite faces of the ceramic plates flush with corresponding faces of the plastic body and with adjacent edges of the plates out of contact with each other, coat ing the opposite faces of the ceramic plates and the corresponding faces of the plastic body with a metal ceramic paint of the type settable by firing to a metallic film adhering to the ceramic, and firing the plastic body with the ceramic plates embedded therein to set the paint to a metallic film, the plastic being of the type disintegrating at the firing temperature and leaving the ceramic plates with opposite faces having electrodes thereon.

3. The method of making thin flat ceramic plates having a thickness small compared to both length and width which comprises casting a plurality of spaced apart fired ceramic plates of greater than finished thickness flatwise side by side with adjacent edges of plates out of contact with each other in a flat body of plastic thicker than the plates to produce a composite plastic body having the ceramic plates with edges and opposite faces embedded therein and with opposite faces of the ceramic plates generally parallel to opposite faces of the plastic body, grinding away opposite faces of the composite plastic body to a depth below the opposite faces of the ceramic plates to produce a flat composite plate with both the plastic and ceramic ground to said finished thickness of the ceramic plates and with the edges of the ceramic plates held therein and with opposite faces of the ceramic plates flush with the ground surfaces, coating both the plastic and ceramic portions of the opposite faces of the composite plate with a metal ceramic paint of the type settable by firing to a metal coating, breaking away the plastic to leave individual coated ceramic plates, and firing the coated plates to set the paint to the ceramic surfaces.

4. The method of applying metal electrodes to opposite faces of spaced apart ceramic plates without short circuiting over the edges which comprises embedding the edges of a plurality of side by side ceramic plates fiatwise in a body of plastic with the opposite faces of the ceramic plates flush with corresponding faces of the plastic body and with adjacent edges of the plates out of contact with each other, coating the opposite faces of the ceramic plates and the corresponding faces of the plastic body with a metal ceramic paint of the type settable by firing to a metallic film adhering to the ceramic, breaking away the plastic to leave individual coated ceramic plates, and firing the coated plates to set the paint to the ceramic surfaces.

5. The method of applying metal electrodes to opposite faces of a ceramic plate without short circuiting over the edges which comprises embedding the edges of the plate in a body of settable material with the edges of the plate embedded in the body and with opposite faces of the plate flush with corresponding surfaces of the body, applying metal coatings over opposite faces of both the body and plate, and separating the coated plate from the body.

References Cited in the file of this patent UNITED STATES PATENTS 365,908 Chatain July 5, 1887 492,588 Rudolph Feb. 28, 1893 2,328,302 Simison Aug. 31, 1943 2,424,835 Luckey et a1 July 29, 1947 2,429,088 Box 1) Oct. 14, 1947 2,429,089 Box (2) Oct. 14, 1947 2,511,962 Barnes June 20, 1950 2,551,712 Soby May 8, 1951 2,563,936 Huntsberger Aug. 14, 1951 2,608,539 Bain et a1. Aug. 26, 1952 2,626,206 Adler et a1. Jan. 20, 1953 2,656,473 Warner Oct. 20, 1953 

1. THE METHOD OF MAKING THIN FLAT CERAMIC PLATES HAVING A THICKNESS SMALL COMPARED TO BOTH LENGTH AND WIDTH WHICH COMPRISES CASTING A PLURALITY OF SPACED APART FIRED CERAMIC PLATES OF GREATER THAN FINISHED THICKNESS FLATWISE SIDE BY SIDE WITH ADJACENT EDGES OF PLATES OUT OF CONTACT WITH EACH OTHER IN A FLAT BODY OF PLASTIC THICKER THAN THE PLATES TO PRODUCE A COMPOSITE PLASTIC BODY HAVING THE CERAMIC PLATES WITH EDGES AND OPPOSITE FACES EMBEDDED THEREIN AND WITH OPPOSITE FACES OF THE CERAMIC PLATES GENERALLY PARALLEL TO OPPOSITE FACES OF THE PLASTIC BODY, GRINDING AWAY OPPOSITE FACES OF THE COMPOSITE PLASTIC BODY TO A DEPTH BELOW THE OPPOSITE FACES OF THE CERAMIC PLATES TO PRODUCE A FLAT COMPOSITE PLATE WITH BOTH THE PLASTIC AND CERAMIC GROUND TO SAID FINISHED THICKNESS OF THE CERAMIC PLATES AND WITH THE EDGES OF THE CERAMIC PLATES HELD THEREIN AND WITH OPPOSITE FACES OF THE CERAMIC PLATES FLUSH WITH THE GROUND SURFACES, COATING BOTH THE PLASTIC AND CERAMIC PORTIONS OF THE OPPOSITE FACES OF THE COMPOSITE PLATE WITH A METAL CERAMIC PAINT OF THE TYPE SETTABLE BY FIRING TO A METAL COATING, AND FIRING THE PAINT COATED FACES TO BURN AWAY THE PLASTIC AND TO SET THE PAINT TO THE CERAMIC PLATES. 